On the basis of recent discoveries demonstrating the high reactivity, regioselectivity, and stereoselectivity, and many unique characteristics of Diels-Alder reactions of vinylboranes, this proposal aims to develop a variety of boron-activated cycloadditions and related reactions. Toward that end, a primary objective is to develop new and useful vinylboranes and related Diels-Alder dienophiles. A second objective is to broaden the demonstrated scope of Diels-Alder reactions with vinylboranes, including the use of highly functionalized dienes and a study of the stereochemistry of intramolecular reactions, in order to gain sufficiently broad-based knowledge of these reactions to allow the planning of their use in complex syntheses. Another goal is to generalize a recent discovery that small amounts of boranes can catalyze Diels-Alder reactions of dienes with unactivated acetylenes. Modest improvements in our catalytic reaction could furnish industrially usable processes. The proposed work will also pursue the development of practical asymmetric reactions. Finally, recent discoveries with a second boron-activated pericyclic reaction, the allylboration of alkenes, suggest a huge and varied direct utility of reactions with alkenes, and many useful new synthetic methods based on secondary conversions of the allylboration products. It is proposed to extensively study the scope of allylborations with the goal of fully developing this new and unique carbon-carbon bond forming reaction. The health-relatedness to the work in this proposal derives from an honest impact on methods for the synthesis of a wide variety of medicinally important natural and artificial substances.